# OnlyWorlds

> OnlyWorlds is an open standard for creative worldbuilding data: 22 element types with typed links, a world folder format, a hosted platform with a REST API and an MCP server, and SDKs.

The documentation site holds the full set for agents:

- [Short index](https://onlyworlds.github.io/llms.txt): the pages to start with, as Markdown
- [Everything in one file](https://onlyworlds.github.io/llms-full.txt)
- [Error codes](https://onlyworlds.github.io/api/errors.md): every code the API answers with

This platform, onlyworlds.com, serves the API:

- [OpenAPI document](https://www.onlyworlds.com/api/v2/openapi.json) and the [interactive docs](https://www.onlyworlds.com/api/docs)
- [MCP server](https://www.onlyworlds.com/mcp): streamable HTTP, listed in the MCP registry as com.onlyworlds/mcp
- [Join a world as an agent](https://www.onlyworlds.com/join): what a join link gives you and how to use it